The clash in Zabul province took place on Tuesday in the Deh Chopan district.

Those killed were a "mix of Taleban and anti-coalition militants", US spokesman Col James Yonts told the Associated Press news agency.

"These were well-trained, well-armed people... not just a rogue group," he said, "and they didn't flee, they stood and fought."

Initially the US said that 20 militants were killed.

But on Thursday Col James Yonts said the number of dead has risen to 40 - the highest from a single battle in nine months - after troops examining the battle scene found more bodies.

The Americans say that they used warplanes and helicopter gunships in support of their troops on the ground.

Six US servicemen and five Afghan policemen were also injured.

The clash began when gunmen fired on coalition forces investigating the beating of a local man, the US said.

Afghan Interior Minister Ali Ahmed Jalali said that the fighting started when militants attacked three local doctors and police tried to free them. He said that the trio were subsequently "freed safely".

'Ambush'

The clash in Kandahar province took place on Wednesday.

The US says that the clashes have been fierce

In the first account, an Afghan defence ministry spokesman said nine Afghan soldiers were killed in an ambush by militants near the town of Spin Ghar.

Correspondents say that marks the worst losses suffered so far by the country's US-trained army. Three soldiers were wounded in the attack.

Later a US military spokeswoman said that planes from the US-led coalition that were called to help the soldiers kill 20 of the attackers.

The US has about 18,000 troops mainly in the south and east of Afghanistan.